Abrading – Precision device or process - or with condition responsive... – With indicating
Reexamination Certificate
2003-01-15
2004-08-03
Morgan, Eileen P. (Department: 3723)
Abrading
Precision device or process - or with condition responsive...
With indicating
C451S036000, C451S053000, C451S063000, C451S007000, C451S104000, C451S106000, C451S113000
Reexamination Certificate
active
06769961
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to semiconductor fabrication and, more particularly, to a chemical mechanical planarization (CMP) apparatus and a method for performing a CMP process.
In the fabrication of semiconductor devices, planarization operations are often performed on a semiconductor wafer (“wafer”) to provide polishing, buffing, and cleaning effects. Typically, the wafer includes integrated circuit devices in the form of multi-level structures defined on a silicon substrate. At a substrate level, transistor devices with diffusion regions are formed. In subsequent levels, interconnect metallization lines are patterned and electrically connected to the transistor devices to define a desired integrated circuit device. Patterned conductive layers are insulated from other conductive layers by a dielectric material. As more metallization levels and associated dielectric layers are formed, the need to planarize the dielectric material increases. Without planarization, fabrication of additional metallization layers becomes substantially more difficult due to increased variations in a surface topography of the wafer. In other applications, metallization line patterns are formed into the dielectric material, and then metal planarization operations are performed to remove excess metallization.
The CMP process is one method for performing wafer planarization. In general, the CMP process involves holding and contacting a rotating wafer against a moving polishing pad under a controlled pressure. CMP systems typically configure the polishing pad on a rotary table or a linear belt. Additionally, a slurry is used to facilitate and enhance the CMP process. The slurry is introduced and distributed over a working surface of the polishing pad. Distribution of the slurry is generally accomplished by a combination of polishing pad movement, wafer movement, and pressure applied between the wafer and the working surface of the polishing pad.
FIG. 1A
is an illustration showing a top view of a conventional rotary-type CMP system
101
implementing a polishing pad
103
. The polishing pad
103
rotates in a direction
104
. A wafer holder
105
attached to a spindle
107
is configured to rotate in a direction
108
above the polishing pad
103
. A slurry manifold
109
is disposed above the polishing pad
103
.
FIG. 1B
is an illustration showing a side view of the conventional rotary-type CMP system
101
. The polishing pad
103
is disposed on top of a rotary table
117
. The rotary table
117
is supported by a spindle
119
capable of rotating in the direction
104
. A wafer
113
is supported above the polishing pad
103
by the wafer holder
105
. The wafer holder
105
is supported by the spindle
107
, which rotates in the direction
108
. During operation, a force
121
is applied to the spindle to cause the wafer
113
to contact the polishing pad
103
. Also during operation, a slurry
115
is dispensed onto the polishing pad
103
from the slurry manifold
109
. As the polishing pad
103
rotates in the direction
104
, the slurry
115
is transported to the wafer
113
.
FIG. 1C
is an illustration showing a top view of the conventional rotary-type CMP system
101
in operation. During operation, the polishing pad
103
rotates in the direction
104
while the wafer holder
105
rotates the wafer
113
(see
FIG. 1B
) in the direction
108
. Slurry
115
dispensed from the slurry manifold
109
onto the polishing pad
103
is transported to the wafer
113
. Not all of the slurry
115
dispensed onto the polishing pad
103
is capable of traversing beneath the wafer
113
. Thus, a slurry buildup
127
occurs at a front edge of the wafer
113
. Due to the rotation of wafer
113
, the slurry buildup
127
tends to wrap around the wafer
113
and becomes excess slurry
129
. As the polishing pad
103
rotates, the excess slurry
129
moves toward and over an outer edge of the polishing pad
103
under the influence of centrifugal force. A similar situation exists in linear-type CMP systems in which excess slurry is thrown from a moving belt pad rotating around a pair of rollers. In general, less than 20% of the slurry
115
that is dispensed traverses beneath the wafer
113
. The slurry
115
contribution to a total consumable cost of the CMP process can range from 60% to 80%. Therefore, a need exists to improve the efficiency of slurry utilization in the CMP process.
In addition to inefficient slurry use, maintaining a uniform temperature distribution across the wafer
113
is also a challenge with the rotary-type CMP system
101
. As the polishing pad
103
traverses beneath the wafer
113
, the polishing pad
103
will be exposed to heat being generated from friction and chemical reactions. As the polishing pad
103
rotates, a lower angular velocity exists at a radius r
1
as compared to a radius r
2
. Thus, a unit surface area of the polishing pad
103
traversing beneath the wafer
113
at the radius r
1
will be exposed to more heat than a unit surface area of the polishing pad
103
traversing beneath the wafer
113
at the radius r
2
. Hence, a temperature variation will develop across the polishing pad
103
from radius r
1
to radius r
2
as the CMP process continues. A similar situation exists in linear-type CMP systems in which a temperature variation can develop across a linear belt pad. However, in the linear-type CMP system, the temperature variation across the linear belt pad is due to a circular surface area of the wafer
113
that is in contact with the linear belt pad. Basically, outer regions of the linear belt pad traverse below smaller segments of the wafer
113
. Thus, outer regions of the linear belt pad are exposed to less heat than inner regions. Hence, a temperature variation will develop across the linear belt pad from an outer region to an inner region as the CMP process continues. Since the CMP process is partially dependent on temperature, having a temperature variation across the rotary-based polishing pad
103
or linear belt pad may adversely affect the CMP process results. Rotation of the wafer
113
and slurry movement can help reduce the temperature variation, but not in a totally effective manner. Therefore, a CMP system is needed in which a more uniform temperature distribution can be maintained across a working surface such as the rotary-based polishing pad or the linear belt pad.
Many conventional CMP pads (i.e., rotary-based pads or linear belt pads) have pores dispersed therein. As a conventional CMP pad is used, inner planes of the conventional CMP pad become exposed, thus exposing the pores. In general, the pores in conventional CMP pads have a mean diameter of about 40 microns ±25 microns (1 micron=1E-6 meter). Many surface feature sizes on a wafer vary from about 0.3 micron to about 20 microns. Hence, the larger pore diameters contained within the conventional CMP pad are not satisfactory to provide ideal planarization. Further, as the pores are not evenly distributed throughout the conventional CMP pad, the surface area contact between the wafer and pad can change as a function of wear, causing uncontrolled variability to be introduced into the CMP process. Additionally, the conventional CMP pad has a root mean square (RMS) surface roughness of about 6 microns, which contributes to non-optimal planarization and surface roughness on the wafer. The RMS surface roughness of the conventional CMP pad also introduces difficulty in obtaining a desired wafer surface planarity as low as 0.01 micron. Thus, there is a need for a CMP pad that does not have large and/or uncontrolled surface properties that limit wafer planarization performance.
In addition to CMP pad surface characteristics, abrasives contained within the slurry (i.e., slurry abrasive) also have an effect on the CMP process. A solgel colloidal abrasive is a common type of slurry abrasive defined by discrete abrasive particles. The solgel colloidal abrasive particles can vary in diameter from 0.04 micron ±0.02 micron to 0.2 micr
Kistler Rodney C.
Owczarz Aleksander
Lam Research Corporation
Martine & Penilla LLP
Morgan Eileen P.
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